1. Field of the Invention
The present invention relates to a video signal processing apparatus.
2. Description of the Related Art
FIG. 8 is a block diagram showing a schematic configuration of a known image capturing apparatus disclosed in Japanese Patent Laid-Open No. 2001-025030. In this image capturing apparatus, an image capturing device 1010 converts an optical image to an image signal, and an A/D converter 1012 converts the analog output from the image capturing device 1010 to a digital signal. A captured-image-signal processor 1014 executes removal of color carrier, aperture correction, and gamma processing on the output data from the A/D converter 1012 in order to generate a luminance signal.
Also, the captured-image-signal processor 1014 executes color interpolation, matrix conversion, gamma processing, and gain control on the output data in order to generate color-difference signals, so that video data in YUV format is created.
A memory interface 1016 includes a writing circuit 1016a and a reading circuit 1016b for a memory 1018. The memory interface 1016 writes the video data from the captured-image-signal processor 1014 in the memory 1018, and reads the video data stored in the memory 1018 and outputs the video data to a display-system signal processor 1020.
The display-system signal processor 1020 separates the video data in YUV format into a luminance component Y and a modulation color-difference component, that is, a so-called modulation chroma component C, and applies the luminance component Y and the chroma component C to D/A converters 1022Y and 1022C, respectively. The D/A converter 1022Y converts the luminance data from the display-system signal processor 1020 to an analog signal, and then a low-pass filter (LPF) 1024Y removes a high-frequency noise component from the output from the D/A converter 1022Y. The output from the LPF 1024Y is applied to a mixer 1026 and an LCD controller 1028. On the other hand, the D/A converter 1022C converts the modulation chroma data from the display-system signal processor 1020 to an analog signal, and then a band-pass filter (BPF) 1024C extracts only a frequency component of a modulation chroma component from the output from the D/A converter 1022C. The output from the BPF 1024C is applied to the mixer 1026 and the LCD controller 1028.
The mixer 1026 mixes the luminance signal from the LPF 1024Y and the modulation chroma signal from the BPF 1024C so as to generate a composite video signal. A video amplifier 1030 amplifies the composite video signal output from the mixer 1026 and applies the signal to a TV monitor 1032. Accordingly, an image captured by the image capturing device 1010 is displayed on a screen of the TV monitor 1032.
The LCD controller 1028 converts the luminance signal Y from the LPF 1024Y and the modulation chroma signal C from the BPF 1024C to an RGB signal in accordance with a sub-carrier frequency of a quartz oscillator 1034, and applies the RGB signal together with a driving pulse to a liquid crystal display (LCD) panel 1036. Accordingly, the LCD panel 1036 displays the image captured by the image capturing device 1010 on its screen.
In this known image capturing apparatus, the dynamic range of the LCD is insufficient to express high and low intensity. In particular, the gradation in high- and low-intensity areas of a displayed image is poorly expressed. Therefore, it is difficult to visually check distortion in high- and low-intensity areas in the displayed image so as to manually adjust exposure or to compensate exposure. In order to overcome this problem, the following method has been used. That is, during a review after taking an image, a high-intensity area is highlighted in order to clearly display the high-intensity area in the LCD.
Hitherto, in order to perform highlight display by using on screen display (OSD), the luminance level of each pixel of natural-image VRAM data is measured, OSD data for highlight display is created based on the measurement result, and then the OSD data is written in a memory. In this method, however, OSD data must be created every time the natural-image VRAM data changes, and thus it takes some time to perform highlight display.
When an electronic viewfinder (EVF) is used, since the rate of displaying images read by an image capturing device is high, an operation of rewriting OSD data for highlight display cannot keep up with the rate. Therefore, highlight display cannot be performed.
Also, at an electronic zoom operation in the EVF, the rewriting operation cannot keep up with the changes of a zoom factor, and thus highlight display cannot be realized.
When an image is zoomed during playback, highlight display cannot be performed in synchronization with the zoomed played back image. Therefore, the highlight display cannot be completed until some time passes after the played back image has been zoomed.